Conventionally, a parabolic antenna having a bowl shape is used in a satellite communication or else; however, recently a radial line slot antenna is developed instead of the parabolic antenna.
The radial line slot antenna is disclosed, for example, in Japanese Patent Publication No. 1-13241. Namely, a pair of metal disks are opposed to each other through a spacing, one of which is formed with slots for power emission. A peripheral metal wall is fitted along edges of these metal disks to form an inner waveguide spacing enclosed by these metal disks and the peripheral wall. A feeding means is provided to feed a power to the waveguide spacing such that the fed power is converged to a central portion of the waveguide spacing from the peripheral wall. The feeding means is comprised of a feeding source connected to the waveguide spacing, and an intermediate metal plate disposed in parallel to the pair of the metal disks such as to leave a gap relative to the peripheral wall within the waveguide spacing to provide a return pass of the fed power.
Generally, with regard to a circular polarized electromagnetic radiation having a certain frequency, there exist a right-hand circular polarization which rotates rightward in a traveling direction, and a left-hand circular polarization which rotates leftward in a traveling direction. However, the conventional radial line slot antenna cannot be used commonly to both of the right-hand and left-hand circular polarizations. Therefore, there is a drawback that a separate pair of antenna must be installed for the right-hand and left-hand circular polarization waves, though these waves have the same frequency.
In view of the above noted drawback, an object of the present invention is to provide a polarization-universal radial line slot antenna which can be commonly used for either of the right-hand and left-hand circular polarizations.